I have worked with SS tubing quite a bit from 1/4" through to 3/4" but have used 3/8 the most. If you can borrow, or buy if your budget allows, Swagelok makes the BEST hand benders on the market. They also have a good book on bending and how to calculate the bends, I would recommend it highly.
Their benders will bend a 3/8 tube 90 deg and the nut, at least the Swagelok nut, will go around the bend. I have not seen another bender that give such a nice bend. They are pricey as is everything from Swagelok but they are the best. Parker makes a great bench mounted bender but they are frightfully expensive and only used by someone doing it every day. Parker's hand benders are good but not as good as Swagelok.
The bend you made looked OK and being in SS should last forever.
Bob Parry